1. Field of the Invention
The present invention relates to a device for controlling the fuel pressure in a direct cylinder fuel injection engine having a high-pressure pump and a fuel pressure-varying means. More particularly, the invention relates to a device for controlling the fuel pressure in a direct cylinder fuel injection engine featuring improved response and stability in the fuel pressure control when the fuel pressure has shifted from a steady state to a transient state.
2. Prior Art
FIG. 9 is a diagram schematically illustrating the constitution of a general device for controlling the fuel pressure in a direct cylinder fuel injection engine, in which a fuel pressure regulator (fuel pressure-varying means) is controlled by feedback so that the fuel pressure in a high-pressure fuel system acquires a target fuel pressure.
In FIG. 9, a piston 2 is provided in a cylinder of an engine, and a combustion chamber 3 is formed over the piston 2.
An intake pipe 4 and an exhaust pipe 5 are communicated with the combustion chamber 3, and an intake valve 6 and an exhaust valve 7 are provided in the ports among the combustion chamber 3, intake pipe 4 and exhaust pipe 5. An injector 8 and a spark plug 9 are arranged in the combustion chamber 3.
Though not diagramed, here, in the intake pipe 4 are arranged an air filter, an air flow sensor, a throttle valve, a surge tank and an intake manifold from the upstream side in order mentioned. In the exhaust pipe 5 is arranged an air-fuel ratio sensor for detecting the oxygen concentration.
The air taken in by the engine 1 is distributed into the intake pipe 4 connected to the cylinders through the air filter, air flow sensor, throttle valve and intake manifold.
Fuel such as gasoline is pressurized by a low-pressure pump 11 and is fed from a fuel tank 10 to a low-pressure conduit 12, and is further pressurized by a high-pressure pump 13 and is fed to an injector 8 through a high-pressure conduit 14.
The high-pressure conduit 14 is communicated with a high-pressure return conduit 14A through the injector 8, and the output end of the high-pressure return conduit 14A is connected to a low-pressure return conduit 16 through a fuel pressure regulator 15.
The fuel pressure regulator 15 increases or decreases the opening degree at the output end of the high-pressure return conduit 14A to adjust the amount of fuel returned to the low-pressure return conduit 16 in order to adjust the real fuel pressure PF (hereinafter also simply referred to as xe2x80x9cfuel pressurexe2x80x9d) of the injector 8 to a target fuel pressure PFo.
The fuel pressure regulator returns part of fuel in the high-pressure conduit 14 back to the fuel tank 10 through the low-pressure return conduit 16 to lower the fuel pressure PF, and further closes the output end of the high-pressure return conduit 14A to raise the fuel pressure PF.
When no exciting current Ri is supplied to the fuel pressure regulator 15, the fuel pressure PF in the high-pressure conduit 14 is adjusted by the urging force of a spring (described later) in the fuel pressure regulator 15.
The fuel of a target fuel pressure PFo supplied to the high-pressure conduit 14 is injected into the combustion chamber 3 through the injector 8 provided for each of the cylinders.
The fuel pressure sensor 17 detects the fuel pressure PF in the high-pressure conduit 14.
The air flow sensor and the throttle sensor in the intake pipe 4 detect the flow rate of the air taken in and the throttle opening degree, and a water temperature sensor 18 detects the cooling water temperature WT of the engine 1.
The crank angle sensor 19 forms a crank angle signal CA that represents the rotational position of the engine 1. The air-fuel ratio sensor (not shown) in the exhaust pipe 5 forms an air-fuel ratio signal that represents the oxygen concentration in the exhaust gas.
The above-mentioned sensors send signals representing the operating conditions of the engine 1 as operating condition data to an electronic control unit (ECU) 20.
The ECU 20 reads operating condition data from the sensors, executes a predetermined arithmetic operation, and sends control signals operated as a result of operation to the actuators.
For instance, the ECU 20 supplies an exciting current Ri to the fuel pressure regulator 15 based on the fuel pressure PF detected by the fuel pressure sensor 17 (and data of various sensors), in order to control the fuel pressure PF.
Though not diagramed here, the fuel pressure regulator 15 is provided with a low-pressure regulator in series to suppress the pulsation of fuel pressure in the high-pressure conduit 14.
As means for varying fuel pressure in the high-pressure conduit 14, there can be used those of various constitutions that have been known without being limited to the high-pressure pump 13 and the fuel pressure regulator 15 shown in FIG. 9.
FIG. 10 is a vertical sectional view illustrating, in detail, the structure of the fuel pressure regulator 15, and in which portions same as those described above (see FIG. 9) are denoted by the same reference numerals but are not described in detail again.
In FIG. 10, the fuel pressure regulator 15 includes an electromagnetic coil 151, a magnetic circuit 152, a plunger 153, a valve 154, a valve seat 155, a through hole 156, a communication hole 157 and a spring 158.
Being excited by a duty control with an exciting current Ri, the electromagnetic coil 151 closes the high-pressure return conduit 14A. The magnetic circuit 152 forms a passage of a magnetic flux generated by the excitation of the electromagnetic coil 151.
The plunger 153 is driven in a direction in which it protrudes when the electromagnetic coil 151 is excited. The valve 154 is integrally formed at an end of the plunger 153. The valve seat 155 is arranged being opposed to the valve 154.
The through hole 156 is formed in the center of the valve seat 155, and an output end of the high-pressure return conduit 14A is connected to the through hole 156.
The communication hole 157 penetrates through the side surface neighboring the through hole 156. The low-pressure return conduit 16 is connected to the communication hole 157.
The spring 158 urges the plunger 153 in a direction in which it protrudes.
Next, concrete steps of adjusting the fuel pressure PF by the fuel pressure regulator 15 shown in FIG. 10 will be described with reference to FIGS. 11 and 12.
FIG. 11 shows basic characteristics of the fuel pressure regulator 15, and FIG. 12 shows basic characteristics of the blow-out amount of the high-pressure pump 13.
In FIG. 11, the abscissa represents the duty value (current value) of the exciting current Ri, the ordinate represents the fuel pressure PF, and the fuel pressure PF increases with an increase in the exciting current Ri (current value) starting from the adjusted pressure RS due to the urging force of the spring 158.
In FIG. 12, the abscissa represents the rotational speed of the high-pressure pump 13 corresponding to the engine rotational speed Ne, the ordinate represents the amount of fuel QF blown out from the high-pressure pump 13, and the blow-out amount of fuel QF increases with an increase in the engine rotational speed Ne (pump rotational speed).
In FIG. 10, when the exciting current Ri is supplied from the ECU 20, the electromagnetic coil 151 in the fuel pressure regulator 15 controls the sucking force of the plunger 153 through the magnetic circuit 152 using the magnetic flux generated by the exciting current Ri.
In this case, the valve 154 is pushed onto the valve seat 155 with a maximum force when the exciting current Ri is maximum (when the duty is maximum).
The fuel pressure PF in the high-pressure return conduit 14A (high-pressure conduit 14) is controlled by the amount of fuel that flows from the output end of the high-pressure return conduit 14A into the communication hole 157 through the hole 156.
Therefore, the amount of fuel flowing through decreases with an increase in the exciting current Ri, and the fuel pressure PF increases. When the current is 0 [A], i.e., when the duty of the exciting current Ri is a minimum (=0%), the opening area between the valve 154 and the valve seat 155 becomes a maximum, and the fuel pressure PF is adjusted to a predetermined value due to the urging force of the spring 158.
As described above, the conventional device for controlling the fuel pressure in a direct cylinder fuel injection engine is equipped with the high-pressure pump 13 driven by the engine, and the fuel of a high pressure is directly injected into the combustion chamber 3 through the injector 8 provided in each combustion chamber 3.
The fuel pressure PF in the high-pressure conduit 14 communicated with the injector 8 is adjusted to an optimum target fuel pressure PFo that is operated by taking the operating conditions such as engine speed and engine load into consideration. That is, the fuel pressure PF detected by the fuel pressure sensor 17 is controlled by the exciting current Ri from the ECU 20 to be in agreement with the target fuel pressure PFo.
When the target fuel pressure PFo sharply changes, for example, when the target fuel pressure PFo instantaneously increases and, then, decreases, however, the fuel pressure feedback operation amount is not properly given, and there may occur over-shooting or under-shooting of the fuel pressure PF.
In order to suppress the over-shooting or the under-shooting, there has been proposed a device for controlling the fuel pressure as disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 11-37005.
When the fuel pressure remains steady during the normal operation, in this case, the output duty of the exciting current Ri is controlled to remain constant, and the fuel pressure PF is so controlled by feedback as to come into agreement with the target fuel pressure PFo.
When the target fuel pressure PFo determined by the operating conditions has changed by more than a predetermined amount, on the other hand, the fuel pressure feedback control is discontinued, and the fuel pressure is controlled based on the fuel pressure feedback amount of when the fuel pressure feedback control is discontinued and on a reference control amount (duty value) determined by the operating conditions at that moment.
Then, the fuel pressure feedback control is resumed when a difference between the target fuel pressure PFo and the real fuel pressure PF converges within a predetermined range (determined depending on the temperature of the fuel pressure regulator 15, applied voltage of when the exciting current Ri is supplied, aging, etc.) and when this state has continued for more than a predetermined period of time.
That is, the fuel pressure feedback control is resumed under the conditions in which the difference between the target fuel pressure PFo and the real fuel pressure PF lies within a predetermined range and continues for a predetermined period of time.
When the difference between the target fuel pressure PFo and the fuel pressure PF does not converge within the predetermined range due to some unexpected cause while the fuel pressure is changing accompanying a change in the target fuel pressure PFo, however, the difference in the fuel pressure does not converge no matter how long period of time elapses since the fuel pressure feedback control remains halted, and the fuel pressure feedback control is not resumed.
According to the conventional device for controlling the fuel pressure in a direct cylinder fuel injection engine as described above, when the target fuel pressure PFo has sharply changed, the fuel feedback control is discontinued until the difference in the fuel pressure from the fuel pressure PF converges within a predetermined range in order to suppress the over-shooting or under-shooting of the fuel pressure PF when the fuel pressure is changing. When the difference in the fuel pressure does not converge within the predetermined range, therefore, the fuel pressure feedback control is not resumed.
The present invention was accomplished in order to solve the above-mentioned problem, and its object is to provide a device for controlling the fuel pressure in a direct cylinder fuel injection engine, which suppresses the over-shooting or under-shooting of fuel pressure under a transient fuel pressure condition in which the target fuel pressure changes by more than a predetermined amount, and reliably converges the difference in the fuel pressure in order to improve the fuel pressure transience control performance.
A device for controlling the fuel pressure in a direct cylinder fuel injection engine of the present invention comprises:
various sensors for detecting the operating conditions of an engine;
an injector for directly injecting fuel into a cylinder of said engine;
a pump for feeding fuel to said injector;
a conduit system for connecting said pump to said injector;
a fuel pressure detecting means for detecting the real fuel pressure acting on said injector;
a fuel pressure varying means for adjusting said real fuel pressure; and
a control means for so controlling the fuel pressure by feedback that said real fuel pressure is brought into agreement with a target fuel pressure; wherein
said control means includes a means for operating the fuel pressure correction amount for variably setting a control gain for controlling the fuel pressure by feedback; and
said means for operating the fuel pressure correction amount changes the control gain when said target fuel pressure has changed by more than a predetermined amount from a first control gain of when the fuel pressure remains steady over to a second control gain for when the fuel pressure changes.
The invention is further concerned with a device for controlling the fuel pressure in a direct cylinder fuel injection engine, wherein the means for operating the fuel pressure correction amount returns the control gain back to said first control gain at a moment when a predetermined period of time has passed from when the control gain is changed from said first control gain over to said second control gain.
The invention is further concerned with a device for controlling the fuel pressure in a direct cylinder fuel injection engine, wherein the means for operating the fuel pressure correction amount returns the control gain back to said first control gain after a state in which a difference between a target fuel pressure and a real fuel pressure lies within a predetermined range has continued for a predetermined period of time.
The invention is further concerned with a device for controlling the fuel pressure in a direct cylinder fuel injection engine, wherein the means for operating the fuel pressure correction amount variably sets said second control gain depending upon the operating conditions.
The invention is further concerned with a device for controlling the fuel pressure in a direct cylinder fuel injection engine, wherein the means for operating the fuel pressure correction amount variably sets said second control gain depending upon a difference between said target fuel pressure and said real fuel pressure.